1. Field of the Invention
The present invention relates to a throttle-opening sensor which is capable of generating at least two detection signals varying in the mutually opposite directions according to the rotation angle of a throttle grip.
2. Description of the Related Art
For example, a throttle-opening sensor, which is used to detect the throttle-opening of a two-wheeled vehicle, is structured such that it detects the rotation angle of a throttle grip mounted on a handle bar and transmits its detection signal to an electronic control unit carried onboard the two-wheeled vehicle. And, the electronic control unit executes a given operation in accordance with the detection signal transmitted thereto and, based on the operation results of the electronic control unit, not only the ignition timing of an engine but also the opening and closing of an exhaust valve are controlled.
Here, the throttle-opening information is greatly involved in safety during the running operation of the two-wheeled vehicle. Therefore, there is required a dual signal system which includes two signal detect portions and, even in case where one of the signal detect portions is out of order, can carry out various controls during the running operation in accordance with signals obtained from the other signal detect portion. A technology using such dual signal system for carrying out various controls based on the throttle-opening is disclosed, for example, in JP-A-10-176581.
According to the above-cited publication, throttle control is executed using a dual signal system by detecting signals provided by a main sensor and a sub-sensor respectively having the mutually opposite-direction characteristics. That is, as shown in FIG. 3 in the same publication, in a graph in which the opening angle of the throttle grip is shown in the horizontal axis and the output voltage is shown in the vertical axis, as the opening angle increases, one sensor falls linearly, whereas the other sensor rises linearly; the two sensors are previously adjusted so that their respective graphs are symmetric; and, the sum of the output voltages in every opening angles is set such that it always provides a constant value (5 V).
Therefore, in case where one of the sensors is out of order, the detected value of the output voltage from this sensor decreases down substantially to 0 to thereby cause the sum of the output voltages to differ, which makes it possible to recognize that one sensor is out of order. In this case, various controls are carried out in accordance with only the output voltage of the other sensor to thereby secure the safety during the running operation of the vehicle.
However, in the above-mentioned conventional throttle-opening sensor, the dual signal system is structured by disposing potentiometers at different positions, which raises a problem that the number of parts increases and the structure of the throttle-opening sensor is complicated. Further, since each of the potentiometers is composed of a unit, the whole structure of the throttle opening sensor is large.
The present invention aims at eliminating the above-mentioned drawbacks found in the conventional throttle-opening sensor. Accordingly, it is an object of the present invention to provide a throttle-opening sensor which not only can reduce the number of parts to simplify the structure of the throttle-opening sensor but also can reduce the size of the whole throttle-opening sensor.
According to the present invention as set forth in a first aspect, there is provided a throttle-opening sensor, comprising a detect shaft rotatable about an axis in conjunction with a throttle grip, a pair of rotation terminals respectively disposed on different positions in the same circle with the rotation axis of the detect shaft as a center thereof, the pair of rotation terminals being rotatable together with the detect shaft, first and second contact pieces disposed on each of the rotation terminals at predetermined intervals in a rotation-radius direction of the pair of rotation terminals, a printed circuit including a first conducting pattern portion printed along sliding loci of the first contact pieces and a second conducting pattern portion printed along sliding loci of the second contact pieces and a resistance portion printed in a sliding range of the first or second contact piece of the first or second conducting pattern portion, and generating a resistance against a current flowing in the first or second conducting pattern portion wherein at least two detection signals variable in mutually opposite directions according to the rotation angles of the throttle grip are generated due to that the first and second contact pieces respectively allow the first and second conducting pattern portions to conduct therebetween.
According to the above structure, in case where the detect shaft is worked with the throttle grip, the pair of rotation terminals are respectively rotated and also the first and second contact pieces allow the first and second conducting pattern portions to conduct therebetween. The current flowing during such conduction is set as an output voltage which corresponds to the rotation angles of the rotation terminals variable due to the resistance of the resistance portion, while the detection signals generated by one rotation terminal and the other rotation terminal vary in the mutually opposite directions.
According to the present invention as set forth in a second aspect, in a throttle-opening sensor as set forth in the first aspect, wherein one of the first and second conducting pattern portions is formed as a circular-ring-shaped portion with the rotation center of the pair of rotation terminals as a center thereof, at least two of the resistance portions are disposed on mutually opposed portions in the circular-ring-shaped portion respectively, and the other is formed on outside of the circular-ring-shaped portion as an arc-shaped portion.
According to the present invention as set forth in a third aspect, wherein the resistance portion is formed by printing carbon on the printed circuit, and resistance value of the resistance portion is variable according to density of the printing.